A friend when asked why he did charity work, answered: “I do it because it makes me feel good. I do it for me not them”. I agree with him. In a sense he is at least honest to himself!
This meshes nicely with a self-signalling conception of morality. If part of the point of behaving morally is to convince yourself that you’re a good person, then once you’re convinced, behaving morally loses a lot of its value.
By coincidence, a few days after reading this study, I found this article by Dr. Beck, a theologian, complaining about the behavior of churchgoers on Sunday afternoon lunches. He says that in his circles, it’s well known that people having lunch after church tend to abuse the waitstaff and tip poorly. And he blames the same mechanism identified by Mazar and Zhong in their Dictator Game. He says that, having proven to their own satisfaction that they are godly and holy people, doing something else godly and holy like being nice to others would be overkill.
via Less Wrong: Doing your good deed for the day.